An example of an image reading device for reading an image printed on a document is disclosed in JP-A-H12-125080, for example. The conventional image reading device is described below with reference to FIGS. 5 and 6 of the present application.
As shown in FIG. 5, the image reading device 100 includes a light source 120 and a light guide 130. The light guide 130 guides light from the light source 120 to an image reading area S.
Specifically, the light guide 130 includes a subsidiary region 130a and a main region 130b. The subsidiary region 130a includes a light incident surface 131 for entrance of the light from the light source 120, and an inclined surface 132 for shifting the traveling direction of the light entering through the light incident surface 131. The main region 130b includes a main reflecting surface 133 for shifting the traveling direction of the light, which traveled from the subsidiary region 130a to the main region 130b, toward the image reading area S, and also includes a light emitting surface 134 for emitting the light toward the image reading area S. As shown in FIG. 6, the main reflecting surface 133 includes a plurality of recesses 135. The recesses 135, spaced from each other in the primary scanning direction (indicated by an arrow AB), shift the traveling direction of the light entering into the recesses 135, toward the image reading area S.
The light source 120 is a light-emitting diode (LED) chip. As shown in FIG. 6, the light passing portion of the light source 120 is positioned right below the center of the light incident surface 131 of the light guide 130 in the primary scanning direction. This arrangement is made for attaining uniform irradiation to the light incident surface 131 with the light from the light source 120.
In the image reading device 100, one way to increase the light irradiation toward the image reading area S (thereby obtaining a high-quality image) is to increase the amount of light emission from the light source 120.
However, the increase in the light emission from the source 120 entails higher power consumption at the light source 120, which is not desirable.